Why is the JP-pump rapidly turning on and off?

The suction line may be leaky, or there is air in the water. Check whether the backflow preventer is present in the suction line and that it is working properly. Only for Hydrojet: The pre-charge in the pressure tank may not be correctly configured. Check the pre-pressure to make sure the adjustment values are in conformity with the operating instructions. Please consult a specialist company for such work.